1. Field of the Invention
This invention relates to the fabrication of magnetic read/write heads that employ TAMR (thermally assisted magnetic recording) to enable writing on magnetic media having high coercivity and high magnetic anisotropy. More particularly, it relates to the use of a plasmon antenna (PA) to transfer the required thermal energy from the read/write head to the media.
2. Description of the Related Art
Magnetic recording at area data densities of between 1 and 10 Tera-bits per in2 (Tbpsi) involves the development of new magnetic recording mediums, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect. This effect is the thermal instability of the extremely small regions on which information must be recorded, in order to achieve the required data densities. A way of circumventing this thermal instability is to use magnetic recording mediums with high magnetic anisotropy and high coercivity that can still be written upon by the increasingly small write heads required for producing the high data density. This way of addressing the problem produces two conflicting requirements: 1. the need for a stronger writing field that is necessitated by the highly anisotropic and coercive magnetic mediums and; 2. the need for a smaller write head of sufficient definition to produce the high areal write densities, which write heads, disadvantageously, produce a smaller field gradient and broader field profile. Satisfying these requirements simultaneously may be a limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that is the case, further increases in recording area density may not be achievable within those schemes. One way of addressing these conflicting requirements is by the use of assisted recording methodologies, notably thermally assisted magnetic recording, or TAMR.
The prior art forms of assisted-recording methodologies being applied to the elimination of the above problem share a common feature: transferring energy into the magnetic recording system through the use of physical methods that are not directly related to the magnetic field produced by the write head. If an assisted recording scheme can produce a medium-property profile to enable low-field writing localized at the write field area, then even a weak write field can produce high data density recording because of the multiplicative effect of the spatial gradients of both the medium property profile and the write field. These prior art assisted-recording methods either involve deep sub-micron localized heating by an optical beam or ultra-high frequency AC magnetic field generation.
The heating effect of TAMR works by raising the temperature of a small region of the magnetic medium to essentially its Curie temperature (TC), at which temperature both its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to produce within that region. In the following, we will address our attention to a particular implementation of TAMR, namely the transfer of electromagnetic energy to a small, sub-micron sized region of a magnetic medium through interaction with the near field of an edge plasmon excited by an optical frequency laser. The edge plasmon is excited in a small conducting plasmon antenna (PA) approximately 200 nm in width that is incorporated within the read/write head structure. The source of optical excitement can be a laser diode, also contained within the read/write head structure, or a laser source that is external to the read/write head structure, either of which directs its beam at the antenna through a means such as an optical waveguide (WG). As a result of the WG, the optical mode of the incident radiation couples to a plasmon mode in the PA, whereby the optical energy is converted into plasmon energy, This plasmon energy is then focused by the PA onto the medium at which point the heating occurs. When the heated spot on the medium is correctly aligned with the magnetic field produced by the write head pole, TAMR is achieved.
K. Tanaka et al. (US Publ. Pat. App. US2008/0192376) and K. Shimazawa et al. (US Publ. Pat. App. US2008/0198496) both describe TAMR structures that utilize edge plasmon mode coupling.
Rochelle, (U.S. Pat. No. 6,538,617) describes an antenna for sensing magnetic fields that employs a ferrite magnetic core.
Burdick et al. (U.S. Pat. No. 6,424,820) teaches a short wave antenna comprising wire wrapped around a ferrite core.
None of these prior arts address the issues to be dealt with by the present invention.
Referring first to FIG. 1, there is shown a schematic illustration of an exemplary prior art TAMR structure in an ABS (shown as a dashed line) view and in a side cross-sectional view. The dimensional directions in the ABS view are indicated as x-y coordinates, with the x coordinate being a cross-track coordinate in the plane of the medium and the y coordinate being a down-track direction. In the cross-sectional view, the x coordinate would emerge from the plane of the drawing and the z coordinate is in the direction towards the ABS of the head.
The conventional magnetic write head includes a main magnetic pole (MP) (1), which is shown with a rectangular ABS shape, a writer coil (5) (three winding cross-sections drawn) for inducing a magnetic field within the pole structure and a return pole (3). Generally, magnetic flux emerges from the main magnetic pole, passes through the magnetic media and returns through the return pole.
The optical waveguide (WG) (4) guides optical frequency electromagnetic radiation (6) towards the air bearing surface (ABS) (10) of the write head. The ABS end of the write head will be denoted its distal end. The plasmon antenna (PA) (2), which has a triangular shape in the ABS plane, extends distally to the ABS. The distal end of the waveguide (4) terminates at a depth, d, away from the ABS. An optical frequency mode (6) of the electromagnetic radiation couples to the edge plasmon mode (7) of the PA (2) and energy from the edge plasmon mode is then transmitted to the media surface where it heats the surface locally at the ABS edge of the PA triangle.
An advantage of the design illustrated in this figure is that the WG (4) terminates before reaching the ABS of the write head so that leakage of visible radiation to the ABS is reduced. Meanwhile, the energy from the edge plasmon mode (7), upon reaching the ABS, can achieve a spatially confined region that is desirable for achieving a high thermal gradient in the magnetic medium. With the long PA body (2) and large volume of metal composing the PA, heating damage of the PA is also greatly reduced.
In the prior art cited above, the materials used to form the PA are metals like Ag and Au that are known to be excellent in generating optically driven plasmon modes. However, in the prior art a problem still exists in aligning the optical heating profile within the region of energy transfer at the medium surface, with the magnetic field profile generated by the write head.
Referring to FIG. 2, there are shown schematically a typical prior art magnetic field profile (8) and below it, a heating profile (9), such as would be produced by the TAMR writer of FIG. 1 at the position of the heating spot (the peak of the profile) on the magnetic medium. The horizontal coordinate axis in both graphs is the y-coordinate of FIG. 1. The vertical axis is the magnetic field, Hz, in the magnetic field profile and the heat intensity, Pheat, in the heating profile. Both profiles are localized within a small region of the magnetic medium. For reference purposes, the ABS shape of the PA (2) and the ABS shape of the MP (1) (also shown in FIG. 1) are drawn below the axes, so the location of the field and heat transfer can be ascertained.
As can be seen in FIG. 2, the heating spot is at the far leading edge of the magnetic field profile produced by the MP. Although this location will allow sufficient writing resolution with enough heating, it is not the optimal positioning of the two curves relative to each other. To obtain the full benefit of TAMR, the slope of the heating profile (9) should be aligned with the encircled regions of maximum slope (10) or (11), of the magnetic field profile. In this case, a multiplicative factor of the two maximum gradients is obtained.
Due to structural limitations, caused, for example, by the thickness and arrangement of the WG and by choice of the PA design, difficulties in alignments during fabrication, etc., optimal alignment of the heating and field profiles cannot be obtained.